fr en es pt
Contact the author rss astronoo

Acid rain

What is acid rain?

 Automatic translation  Automatic translation Updated June 01, 2013

Rain is naturally slightly acidic because of carbon dioxide it contains.
Acid rain is formed when oxides of sulfur and nitrogen associated with moisture in the air to release sulfuric acid and nitric acid.
These two common air pollutants acidify precipitation. When these substances are emitted into the atmosphere, they are likely to be transported long distances by winds before falling on the ground as acid precipitation (rain, snow, fog or dust).
These acid rain degrade and destroy ecosystems and some old buildings. If acid rain may have a natural origin, during volcanic sulfur emissions, for example, they are primarily anthropogenic, generated by industry, power plants, and of course transportation.
It is believed that acid rain is when the pH is below 5.6 (ph natural rainfall). Acid rain affects forests, animals, buildings, but it also affects our health.


Since few decades that these consequences have become apparent. Although the chemical reactions involved in the formation of acid rain in the atmosphere are complex, are key industrial discharges.

Image: Many volatile chemical compounds such as heavy metals, hydrogen sulfide, chlorine, dioxins and acid gases found in the smoke released into the atmosphere by industry, fortunately less and less in rich countries.

 fumée acide

Measure of acidity


Acidity is measured with the pH scale.
This scale is a measure of the acidity but also basicity liquids, pH 7 for a neutral solution as distilled water.
Each unit of the scale represents an increase of 10 of basicity or acidity. For example, a rain with a pH of 5 is ten times more acidic rain pH 6.
The lakes have a pH close to 7, through the course of the calcium content in soil and water.
This calcium neutralizes acidity but can not absorb an acid rain coming of a highly polluted.
The pH (potential of hydrogen) is used to measure the acidity of water in a value between 0 and 14.


Aqueous solutions including water is the solvent are classified into 3 groups:
- The basic or alkaline solutions are between 7 and 14;
- Solutions neutral pH = 7,
- The acidic solutions: between 0 and 7.

Image: Each unit of the scale represents an increase of 10 of basicity or acidity.

 Measure of acidity

Dying fish


Fish dying by the thousands in lakes in Europa and North America, the first warning given in years 60 and 70, on the destructive effects of acid rain.
Salmon, trout and roach are particularly sensitive to acidification of freshwater.
The most spectacular damage attributed to acid rain are likely to damage suffered in the lakes. In Scandinavia and Canada, few in France, the rains were soon suspected to be the origin of their acidification.
In Vosges, too, there acidification of some streams. When the pH is decreasing, from 5.5 pH values but until very low 4.5 in some cases there has been a change of flora and fauna with a water shortage then fish disappearance of the most sought (salmonids).


When rushes thrive in freshwater reported that abnormal acidity. The foam 'Sphagnum White' can invade lakes forming a thick green carpet on the substance causing the imbalance.


Forest degradation


The forest dieback is a complex phenomenon which leads to a general weakening of the existing trees and stands.
In the 1980s, forests began to die, victims of the fallout of acid rain.
Many forests in Europe were threatened particularly in Germany, Austria, Poland and Romania. One reason for this decline is the removal of soil by leaching of acid rain, nutrients such as magnesium, calcium and potassium, whose trees need to survive. Air pollution in large cities with more than 2 million people also has an impact on forests.
In Beijing, Shanghai, Guangzhou and Shenzhen, mixtures of carbon emissions and automobile exhaust, generate acid rain, more than half of Chinese cities are affected.


Acid rain caused a degradation of soil and groundwater that can lead to the death of trees. Acid rain disrupts photosynthesis by breaking the chlorophyll.
The leaves gradually lose their green color shades to take yellow, orange or red. This is accentuated by the drought.
Their fragile bark becomes vulnerable to insects and diseases.
The species most affected are conifers and conifers.


Degradation of cathedrals


Acidification of precipitation leads to erosion of metallic surfaces such as copper or zinc.
The stones are eroded by rain and wind, but the presence of acid in rain increases their corrosive effect. In addition to high sulfur pollutants can be deposited and then combine with limestone and make the crumbly substance readily solvable by water.
The crust that forms on the surface, stone worsens who ends up starting powder.
Many historic buildings are affected. The Parthenon in Athens traffic was banned, the Colosseum in Rome and most ancient monuments are seriously damaged by acid rain.


Image: While tourists have already noticed this kind of sculpture eroded by the acidity, as to be almost unrecognizable. Here, a sculpture of the castle of Lincoln in Lincolnshire (England).




In the 1980s, industrialized countries aware of the problem, reached an agreement to limit pollution, especially that caused by automobile exhaust.
The cause of these disasters are identified, measures were taken in 1990 at a convention (Clean Air Act Amendment) bringing together scientists, businesses and government bodies.
Appropriate filters were installed on top of chimneys and the acidity of rain decreased significantly, allowing the forest vegetation and aquatic organisms. In 2007 there is much less acid rain in rich countries since the measures taken since the 1980s have contributed to a sharp decrease harmful effects on the environment.


In 2007, in the Vosges, for example, rainfall is less acidic than in the past. The closure of a large number of power plants, smoke filtration plant, the desulphurization of gas oil, contributed to the divide by three sulfur concentration in rainwater on the massive Vosges, between 1993 and 2001. Over the same period, nitrogen oxides were reduced by a factor of two.


1997 © − Astronomy, Astrophysics, Evolution and Ecology.
"The data available on this site may be used provided that the source is duly acknowledged."